The most senior American official to appear at the trial of former Yugoslav president Slobodan Milosevic has testified that the former leader controlled events in Kosovo in 1999. That is the year prosecutors say President Milosevic's forces murdered hundreds of Kosovo Albanians and deported 800,000 others.

Slobodan Milosevic watched intently as the man he considers a major foe entered the courtroom. The last time the two met was in 1998. Mr. Milosevic was then president of Yugoslavia and career diplomat William Walker was the main man in Kosovo for the Organization for Security and Cooperation in Europe.

As head of the organization's Kosovo verification mission, Ambassador Walker's job was to monitor a 1998 cease-fire agreement with Yugoslavia, keeping an eye on troop movements and weapons build-up in the increasingly explosive province.

In all, Mr. Walker had four meetings with Mr. Milosevic over a two-year period. In court Tuesday, he described them as friendly - up to a point. Ambassador Walker said that as soon as he became critical, Mr. Milosevic's behavior turned. He described the former president as someone who refused to hear that his side was breaking the agreement, as a dominating leader who was uninterested in the views of his subordinates. "My impressions were that I was dealing with a person who felt that when he said something, that made it true, that he was not used to being contradicted, that he became defensive when criticized," he said.

Ambassador Walker also testified that Slobodan Milosevic was well aware of what was going on in Kosovo. "In terms of his control over those events, I never wavered in my opinion that I was dealing with the person who was in the maximum control of events in Kosovo, at least from the Serb side," said William Walker.

And it was one of those events that proved the final breaking point for the two men, the murder of 45 Kosovo Albanians in the village of Racak. The alleged massacre in January of 1999 is the first Mr. Milosevic is charged with, and it became a defining moment in the Kosovo conflict.

The day after it occurred, Ambassador Walker was on the scene declaring - on television, that it was a "massacre of civilians." This helped fuel the events and public outrage that ultimately led to NATO's intervention two months later.

In court Tuesday, Mr. Walker described some of the more than 20 victims he found in a Racak ditch as elderly men with white hair, dressed in civilian farm clothes and traditional white skullcaps. He said their eyes had been blown out, the tops of their heads blown away.

Mr. Walker said he saw no evidence of uniforms or weapons or spent cartridges to corroborate the official Serb version that the men killed were terrorists from the Kosovo Liberation Army. He said it seemed to him that the massacre was the work of Serbian Special Forces.

Slobodan Milosevic has already said in court that the whole world knows Racak was a fabrication by William Walker - a pretext to justify NATO's intervention. He will get to put that question to Mr. Walker on Wednesday during a cross-examination he says he is looking forward to.